1. Field of Art
The present invention relates generally to an elastic bushing assembly, and more particularly to improvements in a sealing structure of an elastic bushing assembly suitable as an elastic damper at a pivotal connection in a vehicle suspension system.
2. Discussion of Related Art
An elastic bushing assembly used at a pivotal connection in a suspension system of an automotive vehicle, for example, a control arm bushing used for pivotally connecting a control arm to a member of a vehicle body or chassis, generllly employs a cylindrical elastic or resilient member made of a rubber material, which is interposed between an inner sleeve and an outer sleeve that are disposed in co-axial relation with each other. The elastic member has spring characteristics suitable for mainly absorbing or damping vibrational loads applied thereto in its radial direction, i.e., in the direction perpendicular to the axis of the bushing assembly. However, the use of a relatively hard or stiff rubber material for the elastic member inherently causes the bushing assembly to exhibit relatively stiff circumferential spring characteristic, i.e., hard spring characteristics in the direction of twisting or rotation about the axis of the bushing assembly.
In the light of the above, the use of a sliding member made of a self-lubricating frictionless material between the inner sleeve and the elastic member is proposed to reduce an effect of relatively stiff circumferential spring characteristics of the elastic member. For example, such sliding member is disclosed in U.S. Pat. No. 3,331,642, and Japanese Utility Model Application laid open in 1984 under Laid-Open Publication No. 59-153736. In such proposed bushing assembly, the frictional resistance between the inner sleeve and the elastic member is reduced due to the existence of the self-lubricating frictionless sliding member therebetween, whereby the inner sleeve and the elastic member are comparatively easily rotatable relative to each other. Thus, the sliding member permits the bushing assembly to demonstrate relatively soft circumferential spring characteristics or relatively reduced circumferential rigidity, while at the same time maintaining relatively stiff or rigid radial spring characteristics.
However, a known bushing assembly incorporating such a sliding member suffers from entry of dirts, grits or sludges in between the sliding surfaces of the sliding member and the inner sleeve, and consequent scoring or other damage of the sliding surfaces, or rusting of the inner sleeve which is usually made of a metallic material. Thus, the known bushing assembly indicated above has a drawback that the intended sliding function of the sliding member relative to the inner sleeve is easily deteriorated.
For solving the above drawback, the assignee of the present application developed an elastic bushing assembly as disclosed in U.S. Patent Application Ser. No. 802,051 feld Nov. 25, 1985. This elastic bushing assembly includes (a) an outer sleeve, (b) a rigid sleeve member disposed radially inwardly of the outer sleeve in co-axial relation with the same, the rigid sleeve member having a radial flange which extends radially outwardly from at least one of opposite axial ends of the rigid sleeve member, (c) an elastic or resilient member interposed between the outer sleeve and the rigid sleeve member in integrally fixed relation with the outer sleeve and the rigid sleeve member, (d) an inner sleeve disposed radially inwardly of the rigid sleeve member, (e) a sliding member interposed between the inner sleeve and the rigid sleeve member and slidable relative to one of the inner sleee and the rigid sleeve member, so as to reduce an effect of relatively stiff circumferential spring characterists of the elastic member, (f) a retainer member located at one of opposite axial ends of the inner sleeve corresponding to the radial flange of the rigid sleeve member, and (g) a sealing rubber member held in pressed abutting contact with an axially outer surface of the radial flange of the rigid sleeve member and a surface of the retainer member which faces the axially outer surface of the radial flange, so as to provide sealing between the retainer member and the rigid sleeve member. An example of a sealing rubber member disclosed in the above-identified Patent Application has two radially spaced-apart annular sealing lips whose diameters increase in the axially outward direction of the rigid sleeve member. These outer and inner annular sealing lips have distal end faces which are perpendicular to the axis of the bushing assembly.
In the elastic bushing assembly indicated just above, the sealing rubber member provides excellent sealing between the rigid sleeve member and the retainer member, effectively preventing entry of dirts, grits or sludges in between the sliding member and the inner sleeve and/or the rigid sleeve member, and maintaining the intended sliding function of the sliding member relative to the inner sleeve. Thus, the sliding member properly functions to reduce an effect of relatively stiff circumferential spring characteristics of the elastic member. Further, since the sliding member is interposed between the rigid sleeve member and the inner sleeve which are both comparatively rigid, the sliding member is well protected from deformation or cracking due to external vibrational stresses, and is therefore capable of serving for a longer period of time.
However, the sealing rubber member suffers an inconvenience that its sealing lips held in pressed abutting contact with the retainer member tend to be deflected or warped radially outwardly of the bushing assembly, allowing foreign matters such as dirts, grits or sludges to be accumulated between the retainer member and the warped end of the selaing lips. Consequently, the sealing lips are subject to wear due to abrasion by the foreign matters. Thus, the proposed bushing assembly is not completely satisfactory in terms of the service life of the sealing rubber member and consequently of the bushing assembly.